InternetGetConnectedState 로 인터넷 연결 체크

http://msdn.microsoft.com/en-us/library/aa384702(VS.85).aspx

using System;
using System.Runtime.InteropServices;
using System.Text;

namespace ClassLibrary5
{
 class __InetAvailable
 {
  //HOW TO: determine whether or not there is a connection to the
  //        Internet present on the local machine.

  [DllImport("WININET", CharSet = CharSet.Auto)]
  static extern bool InternetGetConnectedState(
    ref InternetConnectionState lpdwFlags,
    int dwReserved);

  [Flags]
  enum InternetConnectionState : int
  {
   INTERNET_CONNECTION_MODEM = 0x1,
   INTERNET_CONNECTION_LAN = 0x2,
   INTERNET_CONNECTION_PROXY = 0x4,
   INTERNET_RAS_INSTALLED = 0x10,
   INTERNET_CONNECTION_OFFLINE = 0x20,
   INTERNET_CONNECTION_CONFIGURED = 0x40
  }

  static void Main()
  {
   InternetConnectionState flags = 0;

   Console.WriteLine(
     "InternetGetConnectedState : {0} - {1}",
     (InternetGetConnectedState(ref flags, 0) ? "ONLINE" : "OFFLINE"),
     flags
   );
  }
 }
}